Great job. The headbands are so narrow that the ink limitation doesn't really thwart you too much -- you get the idea across just fine, and people will clearly see that it's Donatello before they get close enough to notice any hatching. Plus, your positioning of the faces works nicely. In closing, I want this shirt immensely.

This is the best Tshirt design EVAR. The four color limit is unfortunate. I hope Threadless bends the rules when they make this a design, because I know they will make this a design, because it is simply too friggin awesome NOT to be a Threadless design.

I must admit, it looks so much better on a green background.
But the different background inevitably meants that there are more colours... and I'm not sure that the threadless crew will stretch to 6. Anyway, for those that requested it, here it is.

You know, the more I look at this the more I really -like- the white. It's subtler than green would be, and it fits better with the drawing style you used. Hell, I'm just justifying this because I like the shirt so much. :) Best of luck.